Build the browser with Address Sanitizer or SoftBound

Originally created by @intrigeri on #7155 (Redmine)

• https://trac.torproject.org/projects/tor/ticket/10599
• https://developer.mozilla.org/en-US/docs/Mozilla/Testing/Firefox_and_Address_Sanitizer

It requires either clang 3.1 or gcc 4.8. Neither is in Wheezy.

Related issues

• Related to #5802 (closed)
• Has duplicate #12179 (closed)